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MPLS LDP Label Distribution Failure on an NE5000E

Publication Date:  2019-03-27 Views:  159 Downloads:  0

Issue Description

Version: V800R009

Network topology:

Issue Description

As shown in the figure, NE5000Es and Router (third-party device) function as PEs and SW-1 and SW-2 (third-party devices) function as CEs. NE5000Es exchange VPNv4 routes with Router and an MPLS tunnel is established. When the problem occurs, NE5000E-1 fails to communicate with SW-1, but NE5000E-2 can communicate with SW-2.

On Router, R&D engineers of the peer vendor check the public network LSPs established with NE5000E-1 and NE5000E-2. The incoming label assigned for the FEC of loopback3 (IP address of by NE5000E-1 is an implicit null label (with the value of 3). Therefore, the problem is caused by an abnormality in public network label distribution on NE5000E-1. This conclusion is contained in the troubleshooting report, which is unfavorable for Huawei devices.

Handling Process



     1.Check device configurations.

interface eth-trunk1

 ip address

 ospf cost 100


 mpls ldp

MPLS and MPLS LDP are enabled on the public network-side interface, and the configurations are correct.

     2.On NE5000E-1, check the public network label distributed to R1.

[~CQSZF-ZF_rNE5000E-01]display mpls lsp | include  


                 LSP Information: BGP  LSP



                 LSP Information: LDP LSP

-------------------------------------------------------------------------------    3/NULL     -/-

It is found that the incoming label assigned by NE5000E-1 to IP address is an implicit null label (3).

     3.It is suspected that the label is assigned by another device because only NE5000E-1 and NE5000E-2 are the MPLS LDP peers. Therefore, check the LSP configuration on NE5000E-2.

[~CQSZF-ZF_rNE5000E-02]display mpls lsp | include 


                 LSP Information: BGP  LSP



                 LSP Information: LDP LSP

-------------------------------------------------------------------------------    1653/3     -/Eth-trunk1

It is found that the outgoing labels of the peer vendor's devices are assigned by NE5000E-2.

    4. On peer vendor's devices, check the routes destined for IP address It is found that the next hop is the interface connecting to NE5000E-2. It is confirmed that the peer vendor plans the connection with NE5000E-2 as the primary path and all the upstream traffic is forwarded through NE5000E-2. Therefore, the peer vendor's conclusion in the test report that the fault is resulted from the label distributed by NE5000E-1 is incorrect. It is recommended that traffic statistics be collected when the fault occurs. The data collection result shows that packet loss occurs on the peer vendor's device.

Root Cause

Packet loss occurs on peer vendor's devices.